As a conventional sway prevention control technology for a suspended load, for example, the “sway angle damping control method” as described in Patent Document 1 is known.
FIG. 8 is a block diagram of a travel motion drive control device 220 described in Patent Document 1.
A speed command signal from a speed commander 221 is inputted to a linear commander 222 and a lamp-like speed command NRF0 is obtained. Either an actually measured sway angle θ detected by a rope sway angle detector 229 or a sway angle Eθ calculated by a rope sway angle calculator 238 is selected by a selector switch 239. Now, using the sway angle Eθ calculated by the rope sway angle calculator 238, a damping compensation signal NRFDP can be represented as follows:NRFDP=Sway angle calculated value Eθ×2δg/(ωeVR),
where
“δ” is a damping factor,
“g” is gravitational acceleration (9.8 m/s2),
“VR” is a trolley carriage speed (m/s) corresponding to a motor rated speed,
“ωe” is a rope sway frequency, ωe=(g/Le)1/2 (rad/s), and
“Le” is a measured length (m) of the wound rope.
By subtracting the damping compensation signal NRFDP obtained as mentioned above from the aforementioned speed command NRF0, a speed command signal NRF1 can be obtained. Thus, the difference between the obtained speed command signal NRF1 and the speed feedback signal NMFB detected by the speed detector 226 is inputted to the speed control device 223 equipped with an integrator having proportional gain A and time constant τ1s to be amplified to thereby output a torque command signal TRF.
Furthermore, a speed command signal TRF is inputted to an electric motor torque control device 224 that controls an electric motor torque with the first-order lag time constant τT to control the torque TM of the driving electric motor to thereby control the speed of the driving electric motor.
The speed feedback signal NMFB is created from the rotation speed NM of the electric motor via the first-order lag element 226. The reference numeral “225” denotes a block showing the mechanical time constant τM of the driving electric motor, and “NM” denotes a speed (p.u) of the electric motor. “227” denotes a block showing a movement model of a sway angle of a rope, and “228” denotes a block showing a model of a load torque TL (p.u) of the electric motor. The speed feedback signal NMFB from the first-order lag element 226, the torque command signal TRF, and a hoisting load-weight measured value mLE are inputted to the rope sway angle calculator 238, and the sway angle Eθ is calculated using the formula shown in Patent Document 1.
As explained above, for example, in container cranes, sway prevention is realized by performing the speed control using a value, as a new speed command NRF1, obtained by subtracting a value obtained by multiplying 2δg/(ωeVR) [where, “δ” is a damping factor, “g” is gravitational acceleration (9.8 m/s2), “ωe” is a rope sway frequency (rad/s): ωe=(g/Le)1/2, “Le” is a measured length of the wound rope (m), and “VR” is a trolley carriage speed corresponding to a motor rated speed (m/s)] by a rope sway angle detection signal or a signal obtained by the rope sway angle estimation calculation from the speed command NRF0 passed through a linear commander 222.
In an unloader or an overhead crane, however, it was generally difficult to mount a sway angle detector 229 thereon due to the structure thereof.
Furthermore, in calculating the rope sway angle, the calculation was complicated and cumbersome since, for example, the weight and the frictional coefficient of the trolley carriage or the suspended load were needed for the calculation to eliminate the frictional resistance component.
Further, the measurement of the length of the wound rope Le was needed to obtain the angular frequency ωe, which also makes the calculations cumbersome.
Given the situation above, a simple and easily adjustable sway prevention control method with less measurement items was desired for unloaders and certain overhead cranes with nearly same operational patterns and almost no suspended load weight changes.    [Patent Document 1] U.S. Pat. No. 5,495,955    [Patent Document 2] Japanese Patent No. 3,173,007    [Patent Document 3] Japanese Unexamined Laid-open Patent Publication No. 2004-187380, A